559 FXUS63 KDTX 200845 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 445 AM EDT Sun Jul 20 2025 .KEY MESSAGES... - Dry with seasonable temperatures through Tuesday. - Hot and humid Wednesday and Thursday with heat index approaching 100 degrees possible on Thursday. - Low chance of showers and thunderstorms north of I-69 Wednesday. Higher and more widespread chances Thursday and Friday. && .AVIATION... Chaotic LIFR/IFR/MVFR low clouds across southeast Michigan as weak cold front sinks south. Brief light shower possible near the start of the taf period across the southern tafs before the front clears. Light northerly winds then take hold today with MVFR clouds late in the morning continuing to slowly lift and begin to dissipate in the late afternoon as drier air filters in. Clear to mostly clear skies for tonight with very light northeast winds. As such, some marine influence could produce light fog/low clouds, but confidence is very low and best chance would be FNT & PTK. For DTW/D21 Convection...Thunderstorms are not expected. THRESHOLD PROBABILITIES... * High in ceilings aob 5000 feet into the afternoon hours. Low this evening. && .PREV DISCUSSION... Issued at 346 AM EDT Sun Jul 20 2025 DISCUSSION... Weak low pressure system and cold front are working through the state this morning. Ample low level moisture with dewpoints topping 70 degrees is supporting high coverage of low clouds and isolated spots patchy fog. Cold front will settle south of the state towards the end of the morning and settle towards the Ohio Valley for the afternoon and evening. Combination of diurnal mixing and arrival of dry air will help lift lower clouds through the morning, though the cooler northerly flow should maintain a decent coverage of clouds through much of the day. The influence of a high pressure centered towards Lake Superior today will increase the stable conditions locally and bring a mostly dry forecast. The one expectation may be along the southern border where showers and possibly a brief thunderstorm may graze the state line given the proximity of the front and convection being supported along the front throughout the day. Lower PoPs up to 20 pct will cover this. Post frontal airmass will drop high temperatures today back down to the average or a few degrees below (upper 70s to low 80s). There will be an expansion of the upper level ridge from the Mississippi River Valley to the Great Lakes into the middle of the week while the surface high pressure slides east Tuesday towards the Atlantic. The result will be a warming trend early to mid week. The increasing south to southwest lower level flow will usher in 850 mb temperatures to 20C or greater by Wednesday bringing highs to around 90. Solid moisture advection will also accompany the heat with dewpoints increasing well into the 60s to 70 degrees. The strength of the ridge should keep most of the area dry through Wednesday, though lower end PoPs will remain in the forecast across the Tri- Cities and northern Thumb as shortwaves trigger a possible convective complex that will ride the northern end of the ridge and mainly impact northern MI and parts of northern lower MI. Another hot and humid day may be in store for Thursday. However, highs into the 90s each day will ultimately depend on what the overall cloud cover and evolution of precipitation ends up being given the nearby chances Wednesday and the mid to late day chances on Thursday. Thursday into Friday prospects for precipitation look better as Canadian troughing will draw a cold front trough the Great Lakes and should support the best chance for rain during the week. MARINE... Quiet marine conditions take over behind a cold front today. Northerly winds also prevail as high pressure begins to build in over the area. The high pressure will hold across the region through Monday into Tuesday keeping drier conditions and lighter winds in place. Winds slowly veer to the east as a warm front look sot move in from the Midwest. This will bring the next chances for thunderstorms Tuesday night into Wednesday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....SF DISCUSSION...AA MARINE.......AA You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.